Visuals:
He would look like a stereotypical fat Italian chef (google image search it) with a really big and awesome mustache.

Abilities:
Regurgitate would almost stay the same, except maybe it would look more like pizza sauce and he would clearly be puking on you. I do not imagine Demonic Pathogen changing much visually, maybe incorporate cheese-like visuals. Corpse conversion would only show visual differences in the minions. Minions would be changed into fat Italian sausages. Lastly, Hell on Newerth would simply be reanimated to be a giant pizza that spawns and grows. the more charges, the more toppings there are on the pizza, or simply, the more Italian sausages there are to attack and explode.

Audio:
He would being singing/talking in Italian, pretty simple. Maybe somehow incorporate someone sounding like Dean Martin saying "Balphagore" as he uses Regurgitate or Hell on Newerth. His simple demonic laughs would be replaced by Italian rambles.

-Other Suggestions:
Part of Frostgore's suggestion for Hell on Newerth, the sound would be Balphagore yelling "SAUCE ON NEWERTH!"

commander of death balphagore give him a dark human look , skinnier and a little like zoro
Q change it to green/black poison coming out of his mouth
W same thing
E he lifts up his arm in the air and 5 rats or somethingspawn
R same thing just change it to black/ darker red and change the minions to rats or something

Totally "inspired" in the Top Chefs, one of my favorit shows. A well dressed Chef, Hat'n'all. Voices always mad and sending everyone out fo the cousine. ALES COUSINE!!!!

Q - Sprays Chantilly on the enemies slowing them down and damaging them (since the chantilly is cold). And that teach us that desert is always best served cold... or it is vengance... meh...

W - Scream madly at the contester until his ears hurt, making him angry to his friends, and tought, making them mad and with hurted ears also.

E - Scavenge the corpses to get more... let say... "ingredients" for cooking... eheheheh, sometimes you just dont want to see the chef cooking... When used, spawn little Bellboys and waiters to help the chef!

R - And of course, Main Course, where in the AOE of the ult, the Heroes affected get "served" by waiters food, making them unable to move, after all, its not good for health to walk while you eat.

My idea is a 2 legged demonic crocodile that can spew magma and small reptilian imps from its stomach. It has many horns and can bite with its mouth and mangle its foes with its claws. It has a large stomach similar to Balphagore. It walks in a sort of waddle motion with its head forward, searching for its next meal. It often opens its maw and snaps it shut when it's idling.
It's voice is very reptilian, very similar to myrmidon, but it also with growls,roars, and groans about its endless hunger.
This is the Balphadile.

This demonic reptile crept out of one of the most volatile pits of hell and found its way to Newerth from the smell of chaos and corpses that . It is born of pure fire and brimstone and is hungry for flesh. It's insatiable hunger can not be calmed. It spews charred bone and magma from its gullet, burning the flesh of its enemies, making it all the more hungry.

Regurgitate:The Balphadile spews magma and charred bone from its last meal.
Very similar, but with black bones and soot added to it.

Demonic Pathogen:The Balphadile infects its foes with a virus that festers in its gut, preventing them from casting spells as it spreads.
Could use the same animation.

Corpse Conversion: The Balphadile spews out small reptilian imps that survive within it, as it eats more imps will emerge from within it.
These are small quadrupedal crocodiles. The are set aflame and have soot in many places on their scales.(From swimming in magma within the Balphadile)

Hell on Newerth: The Balphadile is extremely volatile and its volatility increases as enemies cast spells near it. After enough power has built up, the Balphadile can release a huge explosion of fire, magma and smoke, devastating all around it.